The present invention generally relates to visual display systems and methods and, more specifically, to a visual display system utilizing holographic collimators.
According to U.S. Pat. No. 6,152,739, assigned to the Assignee of the present invention, visual display systems are commonly used to simulate training environments where training through actual operations would be dangerous, expensive or otherwise impractical. One common application for visual display systems may be flight simulation and training systems. A typical flight simulation and training system requires visual xe2x80x9cout the windowxe2x80x9d images simulating the terrain, landscape, cultural features such as buildings, roads and bridges, vehicles, and other aircraft in the simulated vicinity of the trainee. One form of conventional flight simulator includes the projection of images onto the inside of a large spherically-shaped dome or partial dome structure. The images are displayed inside the domes using video projectors and associated optical devices mounted inside the domes. These projectors and optics must be carefully positioned inside the domes in order to properly display the simulated images. Another conventional form of a flight simulator typically includes one or more flat video display screens onto which video images are projected by one or more conventional video projectors. The video images may be projected onto the display screens from either the front or the rear of the screens. An example of such a conventional flight simulator may be the Visual Integrated Display System (VIDS), manufactured by The Boeing Company. The VIDS provides four rear-projected video screens positioned a few feet from the trainee used to display simulated images in front of the trainee and up to three additional rear-projected display screens used to display simulated images behind the trainee. Conventional flight simulators also usually include displays and indicators to monitor the simulated aircraft status, and controls, such as a stick and throttle for providing input to the simulation controller in response to the displayed video images. The displays, indicators, controls and other elements of the surrounding pilot environment are often realistic simulations of the environment present in the actual aircraft. Thus, the operator can simulate the flight of an aircraft and can respond to what is depicted by the simulated image on the visual display and to the other displays and indicators.
One primary objective of flight simulators may be to enhance and optimize the simulated images to present the operator with a high fidelity and realistic training environment. Problems experienced by conventional flight simulators, especially those incorporating conventional video projection systems to display the simulated image, include lower than desired brightness and contrast, and a low resolution of the projected images. These problems arise in large part because of the capability of conventional video projectors, and the use of a relatively small number of video screens (necessitating that each video projector project a relatively large image). Additionally, conventional flight simulators generally provide a simulated image that may be focused relatively close to the trainee""s eyes, and not at a far distance, which hinders the perception of depth and results in incompatibilities with other aircraft equipment such a head-up display (HUD) and a helmet mounted display (HMD). An improved flight simulator would produce a virtual image that may be focused at or near infinity so that the virtual image appears sufficiently real to the simulation pilot and would be compatible with a HUD and an HMD. Such an improved flight simulator would be of great assistance to both air-to-air and air-to-ground military combat training, which require eye-limiting resolution, i.e., display resolution that meets or exceeds the resolution of the human eye. Another drawback to conventional flight simulators may be the size of the projectors, display screens, and associated electronics and optics. An improved flight simulator would have a reduced overall size, allowing the entire simulator to be located in a small room, thus reducing the cost of installing and operating the flight simulator.
Such an improved flight simulator, described in U.S. Pat. No. 6,152,739, includes a visual display system that comprises video image generation and display modules. Each module includes: an image generator, a video display operatively connected to the image generator, and adjacent lenses. Each lens may be associated with one module and positioned between the operator and the video display so that the operator views the composite display image displayed on the video displays through the lenses.
Unfortunately, the past methods and apparatus (including the aforementioned prior art improved flight simulator) for producing display images have disadvantages. There are problems associated with using lenses. For example, conventional lenses of the size needed by the visual display system of the present invention are expensive and difficult to manufacture. In addition, if the lenses were expected to have achromatic properties, which describes a characteristic in which light of all wavelengths is refracted to the same degree, a combination of convex and concave lenses, each with different indexes of refraction, would need to be used thereby adding to the difficulty and cost of manufacture.
Fresnel type lenses, which are most preferably used by the prior art display module to present a collimated image to the observer, generally are poor devices for this function. To collimate is to bring into line or make parallel, which is a close approximation of the nature of rays of light reaching an observer""s eyes from a point on a distant object or image. To collimate an image to make it appear at a large distance, for example, is to bring it closer to the ideal condition of all waves emanating from a specific point on the image being exactly parallel. The interpretation of this parallelism as representing distance is a xe2x80x9clearnedxe2x80x9d characteristic of the human visual system.
Problems associated with using a Fresnel lens (which is a single element piano-convex lens which has been divided into concentric rings, with each ring collapsed to a common plane parallel to the piano side of the lens) include the same chromatic problems as for the aforementioned simple lenses, resulting in color smearing of an image viewed through the lens. This also results in a loss of image clarity. The color smearing of a single element lens is well understood. Also, a Fresnel lens (which usually is a special case of a simple plano-convex lens) includes a curved surface that may be divided into a usually uniform set of annular rings. Each ring may then be collapsed toward the piano surface of the lens, producing a thin piece of material that exhibits the light bending properties similar to that of the original, much thicker lens. Collapsing the rings produces a set of concentric grooves separated by walls standing in the direction of the central axis of the lens. The grooves, and particularly the walls separating the grooves, result in degeneration of image quality due to diffraction and shadowing of rays hitting the walls.
Additionally, while a Fresnel lens makes a good collimator for single point sources of light energy, it may be a poor collimator of a two dimensional image. A Fresnel lens characteristically produces a high degree of image distortion as the eye""s viewpoint of the image moves off the central optical axis. This can result in both a vertical shift and a horizontal shift of the image as viewed by the right eye versus the left eye. While the human visual system is somewhat tolerant of a horizontal shift, it is highly intolerant of a vertical shift. Further, for a display system comprised of an array of Fresnel lens devices, images in adjacent optical fields move in opposite directions relative to each other at the junction of the adjacent optical fields as a function of head motion, making it impossible to maintain registration of adjacent, otherwise contiguous, images.
Another limitation of the prior art visual display system, and of compact visual display systems in general, may be the inability to train operators in a realistic front and rear two person cockpit, sometimes referred to as a tandem cockpit, while providing a collimated image to both. To date, the most practical approach would be to place the tandem cockpit within a large radius dome, with a radius large enough to provide the appearance of collimation. There are several disadvantages to this approach. In order to approach adequate collimation performance, these domes may require a radius of 20 feet or more. This large size results in a relatively dim, low contrast, image on the surface of the dome and requires a large facility to house the equipment. With conventional video display systems, such as the one previously described in U.S. Pat. No. 6,152,739, separate visual systems are required for both pilots in the tandem cockpit. The disadvantage of such an approach results in the rear pilot""s inability to view the actions of the front pilot, nor is either pilot able to provide non-verbal communications with one another necessary for crew coordination training. Additional disadvantages of the previously described approach are the increased cost of providing two separate cockpits instead of one combined cockpit, and the increased cost of a larger facility space in which to house the separate cockpits.
As can be seen, there is a need for an improved apparatus and method that displays video images, reduces color smearing and increases image clarity and quality, may be a good collimator of a two dimensional image, can maintain registration of adjacent, otherwise contiguous, images as a function of head motion, and provides the ability to train pilots in a realistic tandem cockpit environment.
In one aspect of the present invention, a visual display system comprises an image generator and a plurality of adjacent video display modules. The image generator may be adapted to generate a video image viewable by an operator of the visual display system, where the video image may be representative of a portion of a composite display image. The plurality of adjacent video display modules include displays that may be adapted to display the portion of the composite display image, where the video display may be remotely coupled to the image generator and may be responsive to the video image generated by the image generator. The video display modules further comprise a plurality of holographic analogs of collimating mirrors (hereinafter called holographic collimators), each of the holographic collimators associated with each of the modules and positioned between the operator and the video display, where each of the holographic collimators allows the operator to view a portion of a display area of the video display module with a degree of head motion. The holographic collimators associated with adjacent modules are joined together along their edges and positioned to tessellate a sphere partially surrounding the operator, thereby permitting the operator to view the composite display image displayed on the plurality of video display modules through the plurality of holographic collimators and perceive the composite display image as a continuous far-focused virtual image, and wherein the distance of the video image displayed by the video display may be located at substantially half of an effective radius of a holographic analog of the collimating mirrors.
In another aspect of the present invention, a method for displaying images comprises generating a video image representative of a portion of a composite display image by a first module, storing, by a second module, data accessed by the first module to generate the video image, displaying the portion of the composite display image by a third module, and permitting the viewing of the displayed portion of the composite display image through a holographic representation of a fourth module.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.